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51 lines
2.6 KiB
51 lines
2.6 KiB
/**********************************************************************
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* Copyright (c) 2013, 2014 Pieter Wuille *
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* Distributed under the MIT software license, see the accompanying *
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* file COPYING or http://www.opensource.org/licenses/mit-license.php.*
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**********************************************************************/
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#ifndef SECP256K1_ECMULT_GEN_H
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#define SECP256K1_ECMULT_GEN_H
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#include "scalar.h"
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#include "group.h"
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#if ECMULT_GEN_PREC_BITS != 2 && ECMULT_GEN_PREC_BITS != 4 && ECMULT_GEN_PREC_BITS != 8
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# error "Set ECMULT_GEN_PREC_BITS to 2, 4 or 8."
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#endif
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#define ECMULT_GEN_PREC_B ECMULT_GEN_PREC_BITS
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#define ECMULT_GEN_PREC_G (1 << ECMULT_GEN_PREC_B)
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#define ECMULT_GEN_PREC_N (256 / ECMULT_GEN_PREC_B)
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typedef struct {
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/* For accelerating the computation of a*G:
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* To harden against timing attacks, use the following mechanism:
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* * Break up the multiplicand into groups of PREC_B bits, called n_0, n_1, n_2, ..., n_(PREC_N-1).
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* * Compute sum(n_i * (PREC_G)^i * G + U_i, i=0 ... PREC_N-1), where:
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* * U_i = U * 2^i, for i=0 ... PREC_N-2
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* * U_i = U * (1-2^(PREC_N-1)), for i=PREC_N-1
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* where U is a point with no known corresponding scalar. Note that sum(U_i, i=0 ... PREC_N-1) = 0.
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* For each i, and each of the PREC_G possible values of n_i, (n_i * (PREC_G)^i * G + U_i) is
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* precomputed (call it prec(i, n_i)). The formula now becomes sum(prec(i, n_i), i=0 ... PREC_N-1).
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* None of the resulting prec group elements have a known scalar, and neither do any of
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* the intermediate sums while computing a*G.
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*/
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secp256k1_ge_storage (*prec)[ECMULT_GEN_PREC_N][ECMULT_GEN_PREC_G]; /* prec[j][i] = (PREC_G)^j * i * G + U_i */
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secp256k1_scalar blind;
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secp256k1_gej initial;
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} secp256k1_ecmult_gen_context;
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static const size_t SECP256K1_ECMULT_GEN_CONTEXT_PREALLOCATED_SIZE;
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static void secp256k1_ecmult_gen_context_init(secp256k1_ecmult_gen_context* ctx);
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static void secp256k1_ecmult_gen_context_build(secp256k1_ecmult_gen_context* ctx, void **prealloc);
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static void secp256k1_ecmult_gen_context_finalize_memcpy(secp256k1_ecmult_gen_context *dst, const secp256k1_ecmult_gen_context* src);
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static void secp256k1_ecmult_gen_context_clear(secp256k1_ecmult_gen_context* ctx);
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static int secp256k1_ecmult_gen_context_is_built(const secp256k1_ecmult_gen_context* ctx);
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/** Multiply with the generator: R = a*G */
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static void secp256k1_ecmult_gen(const secp256k1_ecmult_gen_context* ctx, secp256k1_gej *r, const secp256k1_scalar *a);
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static void secp256k1_ecmult_gen_blind(secp256k1_ecmult_gen_context *ctx, const unsigned char *seed32);
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#endif /* SECP256K1_ECMULT_GEN_H */
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